Multifiber optical cables, particularly those for use in outside the plant applications in which the cable is exposed to environmental conditions, may include a protective sheath surrounding the optical fibers of the cable. In some instances, these optical cables can also include a non-fiber strength member in the center of the cable, designed to protect the cable from bending more than the approved bend radius of the cable to prevent damage to the cable and loss of optical signal strength.
When multifiber optical cables are routed outside of a building or enclosure, that cable is exposed to environmental extremes, including temperature extremes. These temperature extremes affect the various components of the multifiber cables differently, based on the varying rates at which temperature affects each of the components. For example, in designing the cables, the strength member and the fiber optical fibers within the cable expand and contract at the same rate, but the protective sheath surrounding the optical fibers generally is made from a plastic material which expands and contracts at a higher rate than the fibers or strength member. This phenomena is described in detail in Gebizlioglu, Time- and Temperature-Dependent Material Behavior and its Impact on Low-Temperature Performance of Fiber Optic Cables, (Materials Research Society Proceedings Vol. 531, p. 333 (1998)).
At low temperatures, the protective sheath surrounding the optical fibers contracts, exerting a compression force on the optical strands. This compression force can form microbends in the optical fibers, resulting in signal loss along the length of the optical fiber.